Magnetic positioning and retrieval devices for implantable medical devices may offer advantages with respect to both ease of alignment and engagement; however the presence of magnetically active elements such implantable devices may result in undesirable effects if the patient subsequently requires or would benefit from exposure to strong external magnetic fields such as those employed for Magnetic Resonance Imaging (MRI). In particular, a magnetic element which is not aligned with the external magnetic field may experience a torque tending to twist the magnetic element and the associated medical device. In addition, the misaligned field may tend to demagnetize the magnetic element thereby rendering it less suited for magnetic retrieval. These effects may exclude the patient from certain important diagnostic measures.
These considerations are particularly important for devices such as, for example vena cava filters which are commonly implanted for extended periods of time. Vena cava filters often are emplaced and never retrieved, remaining effective during their time in place, and remaining permanently in place. However, in some cases it may be desirable to remove or reposition a medical filter after it has been in place for a period of time. Retrieval of medical filters can be challenging. One method of retrieval involves use of a catheter with a loop which is pushed out of the catheter and used to snare a hook on the end of a filter. One of the most difficult aspects of vascular and other medical filter retrievals is locating or aligning the correct part of the filter with the operative end or loop of the retrieval catheter. The surgeon is often working through a long catheter extending through a tortuous anatomy while viewing a shadowy image of the filter and retrieval catheter loop in a two dimensional fluoroscopy image. Fluid flow within the vein or body passage may further increase the challenge.
In light of these challenges, it would be beneficial to have an improved device and method for removal or repositioning of vascular and other medical filters. It would also be desirable to have a practical and economical system and method which facilitate removal of medical filters after implantation. It would be further desirable to have a retrieval system and method which can reduce the time required for retrieval and which can be used even under view of a shadowy, two dimensional image. Furthermore it would be desirable to have a retrieval system and method which can be used from either a femoral or jugular approach and which can be adapted for use with a wide variety of medical filter designs.
Further, it would be beneficial to provide implantable medical devices, such as vena cava or other filters, which are both magnetically retrievable from the body and which avoid the difficulties which may be encountered when magnetic elements are subjected to strong external magnetic fields.